This invention relates to a biaxial vent extruder applicable to the processing of waste fluid slurries, radioactive waste fluid or the like.
Recently, the problem of processing of radioactive waste fluid in a slurry has become acute. In the processing of these materials, it is most important to maintain safety conditions. Until the present time, maintenance on land in "vaults" and/or discharge into the ocean have been adopted as methods of processing radioactive waste substances. In these methods, waste substances must be solidified into a form suitable for maintenance or discharge. In general, low level radioactive waste substances are solidified in 200l drum cans. An initial solidifying method used is a cement solidifying type. Recently, asphalt solidifying, glass solidifying and plastic solidifying methods have been developed.
In view of the above developments, it is desired to process the radioactive substances with safety and at low cost.
One of solidifying processes of the radioactive substances, a prior art biaxial vent extruder apparatus, is shown in FIGS. 1 and 2 and well known. However, the prior art apparatus has the following defects.
1. Since the parallel screws extend to the extruding cylinder outlet end, the sealability of the extruding cylinder deteriorates and due to a negative pressure for degassing. Raw materials also tend to be clogged in the outlet thereof.
2. Since means for controlling the flow rate are not provided in each vent, it is very difficult to control the amount of evaporation of each vent port. As a result, the degassing efficiency and hence operationability deteriorate.
3. Since the rotational direction of the parallel screws is the same, the solidification shape of the solidified substances stagnates on one side of the vent port walls. Since carry-over of the solidifying and solidified substances are large, the physical characteristics of the final products are unstable.
4. The solidifying substances and solidified substances are separately introduced into a hopper cylinder. If the solidified substances are introduced to the reduction device side, there is a possibility that the solidified substances will leak from the ground.
5. Since the rotational rate of the screw cannot be maintained at more than 300 rpm, the evaporation efficiency of the waste fluid deteriorates. Therefore, the size of the apparatus tends to become unduly large.
In addition to the radioactive waste fluid a plating waste fluid also in slurry form presents a problem of processing in view of the threat of public pollution. For processing, generally, vacuum dehydration is carried out to thereby produce a sludge. The plating waste fluid is heated and vaporized by the biaxial vent extruder in the same manner as the radioactive waste fluid so that the waste fluid can be solidified using an asphalt. However, the processing using the biaxial vent extruder is disadvantageous as in the processing of the radioactive substances.